Project Summary Zika virus, until recently an obscure mosquito-borne flavivirus from Africa, has emerged rapidly within the past two years as a major threat to public health in the Western Hemisphere. Having traveled across the Pacific, it has become endemic in Brazil and is expanding its territory northwards in South and Central America, Mexico and the Caribbean, carried by a similarly expanding Aedes mosquito population. While Zika virus infection is generally relatively benign in the acute stage, it is suspected based on growing evidence of causing microcephaly in infants born to infected women, and has been linked to Guillain-Barr syndrome and meningitis in other cases. In addition to transmission by mosquito bite, Zika can likely be transmitted by sexual contact and through blood transfusions. The World Health Organization (WHO) has declared Zika to be an international public health emergency, and the U.S. Centers for Disease Control (CDC) and the U.S. Food and Drug Administration (FDA) are actively ramping up efforts to prepare for and respond to the threat posed by Zika in the United States. Accordingly, FDA has advised the temporary deferral of blood donors who have had potential exposure in endemic areas such as Puerto Rico, and has recently approved the use under IND of investigational blood screening assays detecting viral RNA. However, given the very short duration of viremia, most individuals exposed to Zika virus are likely to be negative when tested for viral RNA, and the only means to detect prior exposure and associated health risks is through serologic tests for antibodies to the virus. As the emergence of Zika as a significant human health threat is so recent, there has been no demand for diagnostic assays until now, and commercial products are either non-existent or inadequately validated. This project addresses the critical need for a clinical diagnostic assay for Zika virus infection. The need is further exacerbated by the difficulty in distinguishing Zika from Dengue virus infection given that the two viruses are genetically related, and overlap in mosquito vector and regions of endemicity. In Phase I, we propose to identify peptide epitopes specific for the Zika virus that will enable development of an ELISA allowing accurate serologic identification of Zika infection in individuals beyond the viremic phase, who may also have had exposure to Dengue or other flaviviruses. To accomplish this, we will probe overlapping peptide microarrays derived from Zika proteins with serum samples from individuals with Zika or Dengue infection, confirmed by nucleic acid and immunological assays. Longitudinal sampling from individuals originally identified with acute Zika infection by RNA assays will provide gold standard serum samples with successive IgM and IgG seropositivity for assay development and validation. Immunoreactive peptides will be identified and translated into ELISA test format. In Phase II, we plan to refine this assay into an FDA-cleared, manufactured product for in vitro diagnosis of infected individuals and management and counseling of blood donors.